The invention relates to sensing the direction and rate of rotation of a rotating member and more particularly to a circuit for detecting a rotational direction change on the first edge of a tach pulse that is out of sequence. The circuit also may be used to detect linear motion, i.e., x-y position, direction, etc.
There are various servo systems, particularly in the fields of television, audio, instrumentation, manufacturing, etc., which are employed to control precisely the speed and position of a rotating member such as a reel, capstan, disc, etc., or to control the linear speed and position of a translating member. To provide such control, it is necessary first to detect precisely the direction and rate of rotation of the rotating member. In addition, in very sophisticated systems, it is preferable that detection occurs at a very fast response time.
Typical of rotation sensing circuits are those employed in conjunction with a pair of rotation sensing tachs disposed 90.degree. apart, i.e., in quadrature, which tachs generate two pulse trains with a phase relationship indicative of the direction and a frequency indicative of the rate of rotation of the member. Most of these sensing circuits require one or more pulses from each phase of the two phase tachs before a change in direction of rotation can be detected. It follows that the response times of such circuits are correspondingly compromised, and ambiguous signals are generated in instances where the rotating member experiences multiple direction changes before two tach pulses have occurred.
The invention overcomes the disadvantages of the above movement sensing circuits and may be used in any control system wherein tach pulses indicative of rotational or translational direction and rate are generated.
To this end, an exclusive OR gate compares a preselected short pulse with a waveform which defines the phase relationship between tach A and tach B pulses. In one embodiment the resulting output is fed to a latch along with narrow clock pulses. If tach A leads tach B in phase, the latch input always is high when a narrow clock pulse occurs. If tach A lags, the latch input always is low during the narrow clock pulse. The first edge of tach A or tach B that is out of sequence causes the latch to change states, thus indicating a change in the direction of rotation prior to the occurrence of the next tach pulse.
Thus it is an object of the invention to provide a precision direction sense circuit with very fast response time.
Another object is to provide a quadrature tach decoder circuit which detects a change of rotational or translational direction on the first edge of a tach pulse that is out of sequence.
A further object is to provide a quadrature tach decoder circuit which delivers a clock pulse whose rising edge always occurs after a direction change.
Still another object is to provide a quadrature tach decoder circuit which detects linear motion, i.e., position and direction of a translating member.